1. Field of the Invention
The present invention relates to video enhancement, and more particularly, to a method for handling overlay subpictures in stabilized images.
2. Description of the Prior Art
Image stabilization is a technique used for preventing or eliminating instability in photographic devices, such as telescopes, binoculars, cameras, and video cameras. For devices such as telescopes, which are for observing the subjects in the distance, even a slight shake can cause a major shift in the image displayed. Likewise, for cameras employing long shutter speeds, stillness is necessary for ensuring capture of a clear, focused image with no blur. Thus, image stabilization is a powerful and important tool for helping observers, photographers, and videographers capture steady images without blur.
In the realm of video, image stabilization, which is typically a preventative technique employed at the photographic device, can also be employed as an editing “cure” for instability occurring from frame to frame in an existing video clip. Please refer to FIGS. 1 and 2, which illustrate an example of performing image stabilization according to the prior art. FIG. 1 shows a first frame 101 and a second frame 102 in sequence in a video clip 100. The first frame 101 precedes the second frame 102, and can be considered an image. From the first frame 101 to the second frame 102, observations about certain elements common to a scene being captured in the first frame 101 and the second frame 102 can be made. In the scene, a man 103 is photographed. It can be seen that the man 103 shifts downward from the first frame 101 to the second frame 102. Thus, the photographer either shifted or tilted the camera upward between the first frame 101 and the second frame 102. To stabilize the scene between the first frame 101 and the second frame 102, editing software can be utilized to crop a top portion of the scene displayed in the second frame 102, and fill in a bottom portion 110 of the scene displayed in the second frame 102, so as to maintain a constant resolution throughout the video clip 100. The filling in can be accomplished by utilizing an algorithm to extrapolate from existing data in the second frame 102, or previous data from earlier frames, such as the first frame 101, could also be utilized to fill in the bottom portion 110 of the scene displayed in the second frame 102. At this point, the image is considered stabilized.
In many situations, however, before stabilizing the image, it is likely that the image will have added text or logos, e.g. subtitles or a company logo. This may occur, for example, if the user received the image from another user who has already performed some editing, such as adding the logo or subtitles, or it could occur if the user previously added the subtitles themselves, and decides to perform image stabilization at a later point in the editing process. Please refer to FIG. 3, which illustrates image stabilization with subtitles according to the prior art. A video clip 300 includes a first frame 301 and a second frame 302, which can be considered an image. The image includes a mountain 303, subtitles 304, and a time display 305. Similar to the situation described above for FIGS. 1 and 2, when the editing software is utilized to perform image stabilization on the second frame 302, the second frame 302 is cropped at the top of the scene, and the algorithm is utilized to fill the in the bottom of the scene. However, this time, the subtitles 304 and the time display 305 are shifted up with the rest of the scene, as they are considered part of the scene. This means that as image stabilization is performed over the entirety of the video clip 300, the subtitles 304 and the time display 305 will jump up and down, or left and right, from frame to frame in the video clip 300. This disorients the viewer, rendering the subtitles 304 and the time display 305, and possibly the entire video clip 300, unviewable. Further, this destabilization could be extended to other desirably static items, such as logos and other added effects.